Thermostatic switch and mounting for same



June 18, 1935. R w sc 2,004,963

THERMOSTATIC SWITCH AND MOUNTING FOR SAME Filed June 13, 1932 152 denier? flan JC/LQZ) Patented Junel8, 1935 'rnnnmos'rs'rrc swrron AND uoun'rm roa sum Frank W. Schart, Chicago, 111.,

amino! to McGraw Electric Company, Chicago, 111., a corporation of Delaware Application June 13, 1982, Serial No. 818,84!

9 Claims.

A primary object of this invention is to provide an improved form of thermostatic switch, and particularly one which is slow to'respond to changes of temperature both in opening and in closing so as to make thesame slow acting,

thereby preserving the switch contacts.

Another object is to provide a thermostatic switch which has a slight wiping action between the contacts so as to keep them bright and clean.

Another object is to provide a thermostatic switch with a protective shield to intercept the 7 direct rays from the heating element.

These and other objects, as will hereinafter appear, are accomplished by this invention which is fully described in the following specification and shown in the accompanying drawing, in which- Figure 1 is a side elevation of a waille iron embodying the invention;

Fig. 2 is a partial vertical section through the lower half of the waflle iron showing a thermostatic switch with the contacts closed as when the iron is cold;

Fig. 3 is a partial view showing the thermostat heated with the contacts about to separate;

Fig.4. is the same showing the contacts separated; and

Fig. 5 is a vertical section through an electric iron showing this thermostatic switch applied thereto.

The embodiment illustrated comprises a thermostatic switch which is shown in detail in Fig. 2 wherein it is applied to the lower heating section l8 of a waffle iron which has a pocket ll formed by side walls l2 and a top l3. The thermostatic switch, as illustrated, comprises a support H which is secured to the outside of the top I3, as by means of screws l5, and carries an electrical contact l8 which is insulated therefrom, and which extends through an opening l1, in the top. The support also carries a post 18 which is rigidly secured thereto, and about which is slidably mounted a sleeve l9, the outer end or which is provided with screw threads 28 which engage a nut 2|, the latter being rotatable about an extension 22 on the post and secured in place by means of a screw 23.

Thus it will be seen that the nut 2| by being rotated moves the sleeve in or out with respect to the post, depending on which way the nut is rotated. The nut carries an operating lever 28 which extends through a long slot 25 in the base 28 of thewaflle iron, as shown in-Fig. 1, so as to permit of the adiustment oi the thermostatic switch, as-will later be explained, by means of the adjusting lever 28. The sleeve l8 carriesva bracket 21 to which is secured a first bimetal strip 28, which is preferably insulated therefrom by insulating strips 28. To the outer end of this 5 bimetal strip is secured the outer end of a connecting member 28, the inner end of which is riveted or otherwise secured to a second bimetal strip 88, the latter carrying at its outer end an electric contact it which is adapted to engage the electric contact is so as to pass current therethrough when closed.

The bimetal strip 28 is so formed that heat tends to cause it to move so as to carry it away from the electrical contact l8, while the bimetal strip 88 is so formed that its action is reverse, namely, its curvature under the action of heat tends to force the electric contact 3| toward the electric contact l8. The eiiect of this combination'of oppositely acting or opposed thermostatic elements is as follows: As these two bimetal strips become heated the first strip 28 tends to move away from the fixed contact It. At the same time the strip 38 tends to keep the contact 2| in contact with the fixed contact l8, with the result that these electric contacts are longer in engagement than would otherwise be the case. Finally, however, the movement of the longer strip 28 exceeds the opposing motion of the shorter strip 38, with the result that the contact 3| is moved clear from the stationary contact l6;

It will be observed that when the parts are at room temperature, they have a position similar to that shown in Fig. 2, in which the outer ends of the bimetal strips are relatively close together. As they become heated, however, the bimetal strip "tends to pull away thereby assuming a position shown in somewhat exaggerated form in Fig. 3. After the contacts are separated, as shown in Fig. 4, both bimetal strips begin to cool 01!, with the result that the longer strip 28 tends to bring the contact points back into engagement, whereas the shorter strip 88 again opposes the action of the longer strip 28, thereby tending to keep the contact points out of engagement for a longer period. As a result, this thermostatic switch is slower opening and slower closing than would otherwise be the case, and consequently the number of makes and breaks for any given period is considerably less, with less wear and tear on the contact points.

of motion of the contact points across each other while in engagement. This wiping action has'a tendency to keep these points smooth and bright.

It will be observed that the thermostatic switch is almost completely insulated against direct radiation from the heater element 32, which is connected in series circuit with the thermostatic switch and with the contact pins 33. Since the method of connecting these elements up is well known in this art and forms no part of the present invention, the various leads for doing it are not described in detail. i; 1.;

It is sufilcient to state, however, that the upper heating section 34 (Fig. 1) is similar to the lower section III, except that it carries no thermostatic switch but has a heating element similar to the heating element 32 which is connected in series circuit, with the lower heating element through connections (not shown) within I are also formed integral with the sole plate I05 the sole plate being particularly thin just below this pocket, thereby insuring that the thermostatic switch will be responsive to the temperature of the sole plate. Direct radiation from the heating element 32 is prevented by the side walls II, as in the case of the waille iron. In

this case, however, the nut II is preferably made of a heat insulating material and has a short handle 21". by which it may be turned. This thermostatic switch adapts itself well ,to unit assembly so that it can be built and tested as such, after which it can be readily assembled in the iron or waille mould.

While I have shown and described but a few embodiments of my invention, it is to be understood that it is ,capable of many modifications. Changes, therefore, in the construction and arrangement may be made which do not depart from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In a thermostatic switch, a fixed contact, a support therefor, a first bimetal strip carried at one end by said support, the opposite end carrying a second bimetal strip arranged to move when the two are heated in the opposite. direction from that of the first bimetal strip, an electric contact carried on the second bimetal strip and adapted to engage the fixed contact. the second bimetal strip overlying the outer end portion of the first bimetal strip and spaced therefrom, and an offset connecting member extending between the two bi-metal strips, said member being secured to the outer end of the first bimetal strip and to the inner end of the second bimetal strip.

2. In a device of the class described, a sup-. port having a post, an electric contact carried by the support, a bracket slidably carried on the post, a bimetal strip carried by the bracket and having a contact adapted to be movable into and out of engagement with the first mentioned contact by the movement of the bimetal strip under varying degrees of heat, and means for adjusting said bracketwlth respect to said post for varying the points of opening and closing said contacts.

3. In a device of the class described, a support having a post, an electric contact carried by the post, a bracket, slidably carried on the post, a bimetal strip carried by' the bracket and having a contact adapted to be movable into and out of engagement with the first mentioned contact by the movement of the bimetal strip under varying degrees of the heat, and screw means operable from a point outside the device for adjusting said bracket with respect to said post for varying the points,of opening'and closing said contacts. t

4. In combination, a device "as described in claim 3, a metal plate having-a wall spaced therefrom to form a pocket having an open end, said wall having an opening to receive the fixed contact, and said bimetal strip extending into the pocket through said open end and being shielded by the walls thereof from radiation other than from the plate.

5. In combination, a device as 'describeddn claim 2, a metal plate having a wall spaced therefrom and integral therewith to form a pocket having an open end, said wall having an opening to receive the fixed contact, and said binietal strip extending into the pocket through said open end and being shielded by the walls thereof from radiation other than from the plate.

6. A thermostatic assembly comprising a sup- .sleeve, a bimetal strip carried by the bracket and insulated therefrom, an electric contact carried by the support member and insulated therefrom, an electric contact carried by the bimetal strip, and means for adjusting the sleeve with respect to the post to vary the positions of the contacts.

8. A thermostatic assembly comprising a support member, a post secured thereto, a sleeve slidable on the post, a bracket secured to the sleeve, a bimetal strip carried by the bracket, a connecting member secured at its outer end to the outer end of the bimetal strip, a second bimetal strip parallelto the first secured at its inner 'end to the inner end of the connecting.

member, an electric contact carried by the support member, and an electric contact carried by the outer end of the second bimetal strip.

9. A thermostatic assembly comprising a support member, a post secured thereto, a sleeve slidable on the post, a bracket secured to the sleeve, a bimetal strip carried by the bracket, a connecting member secured at its outer end to the outer end of the bimetal strip, a second bimetal strip parallel to the first secured at its inner end to the innerend of the connecting member, an-electric contact carried by the support member, and an electric contact carried bythe outer end of the second bimetal strip, the two bimetal strips acting in opposite directions upon changes in temperature.-

FRANK W. SCHARF. 

